Method for fabricating solid electrolytic capacitors

ABSTRACT

The instant disclosure relates to an improved method for the production of solid electrolytic capacitor, comprising the following steps. First, provide an insulating substrate. Next, form a plurality of conducting gels including aluminum powder on the insulating substrate. Thirdly, execute a high-temperature sintering process to metalize the conducting gels to form a plurality of aluminum plates. Next, form a dielectric layer on every aluminum plate. Then form an isolation layer on every dielectric layer to define an anodic region and a cathodic region. Lastly, form a conductive layer on the dielectric layer of every cathodic region, thus defining a solid electrolytic capacitor unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The instant disclosure relates to a method for fabricating solidelectrolytic capacitors; in particular, a method for improvingfabrication of solid electrolytic capacitors.

2. Description of Related Art

As technology rapidly evolves in the semiconductor industry, the demandfor products requiring the use of semiconductors as well as thedevelopment of a more advanced, sophisticated electronic componentsbecome increasingly high. Semiconductor technologies such as flip chippackaging technology, laminated substrate design, and passive componentsdesign have an indispensable position in the semiconductor industry.

Take flip chip or ball grid array package structure for example, chipsare configured on and electrically connected to the surface of thepackaging substrate which is aggregated and formed from multiple layersof patterned circuits, and insulating layers. The patterned circuits aremade by etching via photolithography while an insulating layer isdisposed between two neighboring patterned circuits. Furthermore, inorder to obtain the desired electrical characteristics for the packagesubstrate, the substrate is further arranged with passive componentssuch as capacitors, inductors and resistors which may be electricallyconnected to the chips and other electronic components through internalwiring of the substrate.

Among passive components, capacitors are classified according to thetype of electrolyte applied, and can generally be categorized intoliquid electrolytic capacitors and solid electrolytic capacitors. Whilethe life span of the former is determined by the drying time of theliquid electrolyte, the latter uses a solid electrolyte, thereforeeliminating the danger of drying electrolyte and providing a longercapacitor life span.

Traditional surface mounted tantalum solid capacitors usually compriseanode elements made from tantalum powder. However, the tantalum powderin the anode element leads to a relatively high technical threshold. Forexample: in order to increase overall capacitance, small particle sizeis essential to increase the overall reactive surface and consequently,the capacitance.

However, smaller particle size of the tantalum powder requiresadditional processing efforts to achieve. Thus, the smaller the particlesize is required, the more processing is required to produce the desiredsize, and as a result, increases the costs. In addition, tantalumparticles of smaller size make permeation of the cathode agent moredifficult. Furthermore, since only after high-temperature sintering willthe tantalum powder be able to form the tantalum sintered bodies on asubstrate, the high-temperature sintering process required in thefabrication of traditional surface mounted solid capacitor renders theentire fabrication process more complex.

Additionally, prior art illustrates a multi-layer micro-capacitorcomprising a stacked structure of multiple metal layers and dielectriclayers, thus facilitating the miniaturization of capacitors, therebyincreasing the scope of applications. However, such a structure comeswith a higher cost, a high probably of short-circuiting, and a pluralityof complex processes during fabrication and assembly.

To address the above issues, the inventor strives via associatedexperience and research to present the instant disclosure, which caneffectively improve the limitation described above.

SUMMARY OF THE INVENTION

In order to simplify the complexity of the process, reduce manufacturingcosts, and obtain a high yield of the solid electrolyte capacitor, theinstant disclosure provides a method for improving fabrication of asolid electrolytic capacitor. According to the first embodiment of theinstant disclosure, the method includes an insulating substrate havingformed a plurality of aluminum powder containing conductive gel bodies.The conductive gel bodies are arranged in a matrix formation, wherein ascribe line is defined between every two adjacent conductive gels.Thereafter, a high-temperature sintering process is applied on theconductive gel to form a complex aluminum substrate. Next, a dielectriclayer is formed at the surface of each of the aluminum substrate, andthen an isolation layer is formed at each of the dielectric layer todefine an anodic region and a cathodic region. Successively, on each ofthe cathodic region, an electrically conductive layer is formed on thesurface of the dielectric layer resulting in a solid electrolyticcapacitor unit

According to a second embodiment, the improved method includes analuminum powder being cold compressed to form an aluminum pellet,followed by coating the surface of the aluminum pellet with a dielectriclayer, and successively coating a conductive layer on the surface of thedielectric layer.

In summary, one of the embodiments of the instant disclosure, theconductive gel including aluminum powder is formed on the insulatingsubstrate by partial screen printing, and then the conductive gel issintered to form the aluminum substrate. As a result, one skilled in theart can accurately controls the thickness and size of the aluminumsubstrate, enhances the yield of the capacitor, and can also effectivelysimplify the complexity of the manufacturing process. Thus, reducingmanufacturing costs and process time. In the second embodiment, aluminumpellets are formed by cold compressing an aluminum powder without ahigh-temperature sintering process resulting in an anode element withhigher structural strength. Consequently, with such simplifiedmanufacturing process, the complexity, cost, and process time of thecapacitor fabrication are greatly reduced.

In order to further understand the instant disclosure, the followingembodiments and illustrations are provided. However, the detaileddescription and drawings are merely illustrative of the disclosure,rather than limiting the scope being defined by the appended claims andequivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating a method for improving fabricationof solid electrolytic capacitors according to a first embodiment of theinstant disclosure;

FIG. 2 is a cross-sectional view of a method for improving fabricationof solid electrolytic capacitors according to the first embodiment ofthe instant disclosure;

FIG. 3 is a top view of a method for improving fabrication of solidelectrolytic capacitors according to the first embodiment of the instantdisclosure;

FIG. 4 is a flow chart illustrating a method for improving fabricationof solid electrolytic capacitors according to a second embodiment of theinstant disclosure;

FIG. 5 is a cross-sectional view of a method for improving fabricationof solid electrolytic capacitors according to the second embodiment ofthe instant disclosure;

FIG. 6 is a flow chart illustrating a method for improving fabricationof solid electrolytic capacitors according to a third embodiment of theinstant disclosure; and

FIG. 7 is a cross-sectional view of a method for improving fabricationof solid electrolytic capacitors according to the third embodiment ofthe instant disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The instant disclosure is a method for improving fabrication of thesolid electrolytic capacitors especially suitable for the manufacturingof chips. Replacement of tantalum powder with aluminum powder furtherimproves the problem encountered during the fabrication of the tantalumcapacitors, and simplifies the fabrication of the multi-layer capacitor

First Embodiment

FIG. 1 is a flow chart for a first embodiment of the method, and inconjunction with FIGS. 2 and 3, the method is further explained indetails.

Initially, an insulating substrate 10, preferably an aluminum oxide(Al₂O₃) substrate, is provided.

Next, a conductive gel (not shown in figures) including aluminum powderis formed, preferably formed by a thermosetting resin containing fromabout 0 wt % to about 50 wt %, a powder of aluminum containing fromabout 30 wt % to about 100 wt %, and a curing agent containing fromabout 0 wt % to about 50 wt %. The thermosetting resin is preferably anepoxy resin but is not limited thereto. Moreover, to improveconductivity, the particle size of the aluminum powder ranges from 0.05to 5 microns. The aluminum powder can be pre-treated in order to provideuneven surfaces for obtaining more surface areas. The most suitablecuring agent is preferred to be latent curable. Furthermore, theconductive gel may contain inorganic filler from about 0 wt % to about50 wt % to reduce linear expansion. Examples of inorganic fillerscontemplated for use in the conductive gel are silica, aluminum oxide,or aluminum hydroxide. The conductive gel can be formed on theinsulating substrate 10 via techniques such as printing, spray-coating,or similar fashion, and is arranged in a matrix arrangement. Betweenevery two adjacent conductive gels, a scribe line 101 is definedtherebetween for facilitating substrate cutting in the processthereafter. Preferably, the conductive gel is formed on the insulatingsubstrate 10 via partial screen printing for the precise control oflength and thickness of the conductive gel formed, thus reducesfabrication cost and process time.

As the conductive gel is cured (metalized) on the insulating substrate10, a complex aluminum substrate 11 (a sintered body of the conductivegel) is formed on the insulating substrate via a high temperaturesintering process. Preferably, the temperature and the time of the hightemperature sintering process ranges from 300° C. to 550° C., and from0.5 hour to 1.5 hours, respectively.

Moreover, the insulating substrate 10 and the aluminum substrate 11 arechemically treated, preferably anodized in the instant embodiment, toform an oxidized film, preferably an insulating alumina spacer, onto thesurface of the insulating substrate 11, thus forming a dielectric layer12. Furthermore, the chemical treatment may also use electrochemicalformation or chemical solution to control the thickness of thedielectric layer 12 being formed. The dielectric layer 12 of the firstembodiment is produced by an ammonium adipate based, a phosphoric acidbased or the combination solution thereof. An alternative to thechemical treatment of the first embodiment is to immerse the insulatingsubstrate 10 and the aluminum substrate 11 into an electrolyte bath forcross oxidation, heat treating and therefore producing a densedielectric layer 12, preferably an oxidized film.

Furthermore, an isolation layer 13 such as an insulating resin is formedon the center surface of the dielectric layer 12 for isolating an anodecapacitance 15 from a cathode capacitance 16 arranged on two oppositesides of the isolation layer 13, thus defining an anodic region A and acathodic region C on the insulating substrate 10.

In addition, a conductive layer 14 including a conductive polymer layer141, a carbon gel layer 142, and a silver gel layer 143 preferablyarranged in the cathodic region C is formed on the surface of thedielectric layer 12. Specifically, the conductive polymer layer 141 isfirst formed on the dielectric layer 12, then the carbon gel layer 142is formed on the conductive polymer layer 141, and sequentially thesilver gel layer 143 is formed on the carbon gel layer 142 resulting inthe conductive layer 14 and the cathode capacitance 16. The aluminumsubstrate 11 covered by the dielectric layer 12 and oppositely arrangedfrom the cathode capacitance 16 of the isolation layer 13 is the anodecapacitance 15. As a result, a solid electrolytic capacitor unit 100 isfabricated.

Moreover, the conductive polymer layer 141 is formed as a film by evenlycoating a conductive polymer solution onto the surface of the dielectriclayer 12 through a field-effect controlled precision coating technique,thus providing solid electrolytic qualities. The preferred conductivepolymer maybe polyaniline, polypyrrole or polythiophen while the mostpreferred conductive polymer layer 141 is polyaniline. The compositionof the conductive polymer solution includes anilines, oxidants anddopants. The carbon gel layer 142 can be formed by conductive gel,carbon paste. However, the form of the carbon gel layer 142 is notlimited to the samples of the embodiment provided therein.

Furthermore, the solid electrolytic capacitor unit 100 is cut into aplurality of solid electrolytic capacitors 1 by preciously cutting theinsulating substrate 10 conformingly along the scribe lines 101.

Successively, the anode capacitance 15 and the cathode capacitance 16are separately arranged on a lead frame of a supporting member (notshown) to form two opposing electrodes. The solid electrolytic capacitor1 is covered with coating materials such as heat and electricallyinsulating resins, then cured and aged to form a package structure andfacilitate soldering the package structure onto circuit boards viasurface-mount technology (SMT)

Second Embodiment

FIG. 4 is a flow chart and in conjunction with FIG. 5 illustrate asecond embodiment for the method. Foremost, a powder of aluminum isprovided. The aluminum powder may contain a binder such as camphor,stearic acid, polyvinyl alcohol, or naphthalene. The preferred aluminumpowder is formed with the binder while the preferred weight percent ofthe binder ranges from 3 to 5%.

Next, a thoroughly mixed aluminum powder and binder mixture is coldcompressed into a plurality of rectangular parallelepiped aluminumpellets 21 with a compression molding process. Preferably, the coldpress load ranges from 3 to 15 MN/m² to provide the desired bulkdensity. In addition, a lead electrode 211 is inserted within thealuminum powder in a cantilever fashion during the cold press processfor mutually communicating electricity. The preferred lead electrode 211is an aluminum or a tantalum wire but not limited to the examplesprovided therein. The preferred lead electrode 211 in the secondembodiment is a 20 μm aluminum wire to further reduce thickness ofcomponents in a capacitor but not limited to examples provided therein.Moreover, the preferred capacitor fabricated has high capacitance or lowleakage rate. By etching the aluminum powder unevenly and cavernously onthe surface before the cold press process, the surface area of thealuminum powder is increased, thus providing improved capacitance.

The compressed aluminum pellet 21 is further chemically treated,specifically anodized, to form an oxide coating, specifically aninsulating aluminum oxide film, on the surface of the pellet 21, therebyforming a dielectric layer 22. Similar to the first embodiment, thechemical treatment may also use electrochemical formation treatment orchemical solution to control the thickness of the dielectric layer 22being formed. The dielectric layer 22 of the second embodiment isproduced by an ammonium adipate based, a phosphoric acid based or thecombination solution thereof. An alternative to the chemical treatmentof the second embodiment is to immerse the aluminum pellet 21 into anelectrolyte bath for cross oxidation, heat treating and thereforeproducing a dense dielectric layer 22, specifically an oxidized film.

A conductive polymer layer 231 is formed on the surface of thedielectric layer 22, then a carbon gel layer 232 is formed on thesurface of the conductive polymer layer 231, and a silver gel layer 233is formed on the surface of the carbon gel layer 232 resulting in acathode (not marked). Similar to the first embodiment, the aluminumpellet 21 of the second embodiment is formed with a lead electrode 211extruding therefrom in a cantilever fashion and resulting in an anode(not marked). As a result, a conductive layer 23 is formed.

The lead electrode 211 and the conductive layer 23 are separately andelectrically connected to a conductive terminal such as an anode 25 anda cathode 26 through a conductive bonding agent. Successively, the leadelectrode 211, the conductive layer 23, part of the anode 25 and cathode26 are covered by a resin-type coating, cured, and aged to form apackaging structure 24, thereby fabricating a solid electrolyticcapacitor 2 of the second embodiment.

A flow chart in FIG. 6 and FIG. 7 illustrate the third embodiment of themethod in the instant disclosure. Initially, a powder of aluminum issprayed onto a sheet of aluminum and dried through a high temperaturesintering process resulting with a porous aluminum sintered body. Anoxide film is then formed by oxidation on the sintered body resultingwith an anodized foil 31. In addition, a cathodized foil 32 is alsoformed. Please refer to the first embodiment for the preferred time andtemperature of the high temperature sintering process. The aluminumpowder may also include titanium or hydride based sintering agent as theraw aluminum powder. Moreover, preferred examples of the cathodized foil32 may contain carbon, aluminum, and titanium but are not limited to theexamples provided therein.

Next, a preferred spacer 33 or a thin sheet of suitable materials suchas Manila hemp fiber electrolytic paper and a lead electrode 34 arewound between the anodized foil 31 and the cathodized foil 32 to form acapacitor core 30. The preferred spacer 33 material is Manila hemp fiberelectrolytic paper but is not limited to the example provided herein.The preferred thickness of the spacer 33 is from 30 to 60 μm while thepreferred density is from 0.2 to 0.6 g/cm³.

Moreover, the capacitor core 30 is carbonized or similar carbonizationtechniques at a preferred temperature ranging from 200° C. to 300° C.Sequentially, the capacitor core 30 is immersed into an electrolyte bathto form a dielectric layer. Consecutively, the capacitor core 30 isdipped into a polymer solution, and heat treated to cure after removedfrom the solution to form a polymer layer 35 with preferably highconductivity.

The capacitor core 30 is housed by an aluminum cover 36. Then an epoxyresin, a butyl rubber or a preferably suitable sealant packages andseals the capacitor core 30 and an aluminum cover 36 therein whileexposing the lead electrode 34, thus resulting in a package structure37.

Successively, the package structure 37 is cured and aged to form a solidelectrolytic capacitor 3 of the third embodiment. Temperature and timeof the aging process may be adjusted depending on the type, capacity,and voltage of the capacitor.

In summary, the first embodiment illustrates the conductive gelcontaining aluminum powder partially screen-printed onto the insulatingsubstrate 10, and subsequently high temperature sintering the insulatingsubstrate 10 to form the aluminum substrate 11. As a result, thefabrication process is simplified, production time is reduced, and theyield of capacitor is improved through precisely controlling thethickness and length of the aluminum substrate 11. In the secondembodiment of the instant disclosure differs from the first embodimentin terms of the form of aluminum and technique to fabricate thecapacitor, wherein the aluminum powder is cold compressed to form analuminum pellet 21 instead of high temperature sintering. Furthermore,the aluminum powder maybe pre-treated to obtain higher surface area toincrease capacitance of the capacitor while aluminum powder replacestantalum powder to resolve problems generated during the production oftantalum based capacitors. The three embodiments of the instantdisclosure effectively simplify the fabrication of the solidelectrolytic capacitors through altering the physical and chemicalcharacteristics of aluminum powder.

The aforementioned illustrations and detailed descriptions areexemplarities for the purpose of further explaining the scope of theinstant disclosure. Other objectives and advantages related to theinstant disclosure will be illustrated in the subsequent descriptionsand appended drawings.

What is claimed is:
 1. A method for improving fabrication of solidelectrolytic capacitors comprising the steps of: providing an insulatingsubstrate; forming a plurality of aluminum powder containing conductivegel bodies on the insulating substrate, wherein two adjacent conductivegel bodies define a scribe line therebetween; employing a hightemperature sintering process to metalize the conductive gel bodies intoa plurality of aluminum substrates; forming a dielectric layer on eachof the surface of the aluminum substrate; forming an isolation layer oneach of the dielectric layer to define an anodic region and a cathodicregion; and covering the dielectric layer of the cathodic region with aconductive layer.
 2. The method as recited in claim 1, wherein the stepof covering the conductive layer includes steps of: forming a conductivepolymer layer on the dielectric layer of the cathodic region; forming acarbon gel layer on the conductive polymer layer; and forming a silvergel layer on the carbon gel layer.
 3. The method as recited in claim 2,wherein the carbon gel layer is formed by one of the following: aconductive carbon gel, and a carbon based paste.
 4. The method asrecited in claim 1, wherein the aluminum powder containing conductivegel bodies comprises: a thermosetting resin presented from about 0 wt %to about 50 wt %; a powder of aluminum presented from about 30 wt % toabout 100 wt %; a curing agent presented from about 0 wt % to about 50wt %; and an inorganic filler presented from about 0 wt % to about 50 wt%.
 5. The method as recited in claim 4, wherein the particle size of thealuminum powder ranges from 0.05 to 5 g m.
 6. The method as recited inclaim 1, wherein the conductive gel is formed on the insulatingsubstrate via partial screen printing and the temperature and the timeof the high temperature sintering process ranges from 300° C. to 550°C., and from 0.5 hour to 1.5 hours, respectively.
 7. A method forimproving fabrication of solid electrolytic capacitors comprising thesteps of: employing a cold press process to form an aluminum pellet froma powder of aluminum; forming a dielectric layer on the surface of thealuminum pellet; and forming a conductive layer on the surface of thedielectric layer.
 8. The method as recited in claim 7, wherein the stepforming the conductive layer includes steps of: forming a conductivepolymer layer on the surface of the dielectric layer; forming a carbongel layer on the surface of the conductive polymer layer; and forming asilver gel layer on the surface of the carbon gel layer.
 9. The methodas recited in claim 7, wherein the powder of aluminum has uneven andcavernous surfaces.
 10. The method as recited in claim 7, wherein thestep of cold press forming the aluminum pellet includes a lead electrodeto be inserted with the aluminum powder to form the aluminum pellet, anda compression load ranging from 3 to 15 MN/m².
 11. A method forimproving fabrication of solid electrolytic capacitors comprising thesteps of: providing an anodized foil and a cathodized foil; andemploying a winding process for winding a spacer between the anodizedfoil and the cathodized foil along with a plurality of lead electrodesto form a tubular core, in which the anodized foil is formed by a powderof aluminum formed onto a sheet of aluminum, dried, high temperaturesintered to result with a porous aluminum sintered body and forming anoxidized film thereon.
 12. The method as recited in claim 11, whereinthe anodized foil is formed by the powder of aluminum sprayed onto thesheet of aluminum, dried, high temperature sintered to result with theporous aluminum sintered body.